Field of the Invention
Our invention relates to hot strip mills and, more particularly, to hot strip mills employing a hot reversing mill having coiler furnaces on either side thereof as the final reducing stand and having a shape processor immediately downstream thereof.
Description of the Prior Art
Hot reversing mills for plate, sheet and strip having coiler furnaces on opposing sides thereof are employed in semicontinuous mills and as mini mills for processing metal slabs such as steel into a hot rolled product.
The flatness of strip or plate products produced on any type of hot strip mill is critical for most end use applications. The flatness of a strip or plate product produced on a hot reversing mill is particularly critical because a number of passes are taken on the same pair of work rolls and the mill operator does not have the option of decreasing roll crown from stand to stand as the mill operator has on the conventional hot strip mill with five or six finishing stands. The problem of flatness becomes accentuated where a single stand reversing mills comprises the entire mill since as many as 21 passes are subjected to the same crown of the two work rolls. Attempts have been made to develop variable crown rolls and/or employ roll bending, but these efforts have been costly and only marginally effective.
Stretch bend leveling has been employed in the making of very thin metal strip as exemplified by U.S. Pat. No. 4,539,830. Such a system is intended for extremely thin workpieces rolled at unconventionally high finishing temperatures, i.e. 1100.degree. C., which is impractical if not impossible at the intended thickness. Another system for controlling the crowning of plate on a conventional hot strip mill is disclosed in unexamined published Japanese Patent Application No. 55-99611. In that system, an additional light reduction mill stand or plurality of mill stands are added after the final hot strip mill stands and a hot leveler is placed downstream of these auxiliary light reduction mill stands. The plate crown is controlled by changing the amount of crowning of the light reduction mill or mills and the distortion developed is corrected by the hot leveler.